Conventionally, a roller hemming device is widely known that is configured to perform bending (preliminary bending) of a standing flange of a work such as a door subassembly of a car at a predetermined angle by use of a roller, and then to perform bending (final bending) of the flange at a final angle by use of the roller.
As shown in FIG. 5, a work W as a subject to be hemmed by the roller hemming device is a door subassembly. The work W includes a door panel W10 having a plurality of plates, and a door frame W20 projecting upward from the door panel W10 to configure a window frame. When the roller hemming device hems the beltline (the top end of the door panel W10) of the work W, the roller hemming device located in the window frame may interfere with the door frame W20. Therefore, it is difficult to roll a roller along the beltline of the work W.
As shown in FIG. 6, the door panel W10 includes an outer panel W11 which has a standing flange (the right end part of the outer panel W11 in FIG. 6) and which is placed on a bottom die B, an outer reinforcement W12 which is arranged on the outer panel W11 and to the left of the flange, an inner reinforcement W13 which is arranged at a predetermined distance above the outer reinforcement W12, and an inner panel W14 which is placed on the inner reinforcement W13. Since the beltline of the work W has the narrow clearance between the outer panel W11 and the outer reinforcement W12, and the inner reinforcement W13 and the inner panel W14, the roller hemming device interferes with the work W. Therefore, it is difficult for the roller hemming device to hem the beltline of the work W.
Note that FIG. 6 is an end view taken along the line A-A of FIG. 5.
When the beltline of the work W as mentioned above is hemmed, in order to avoid interference with the work W, a roller hemming device having a roller with the small outside diameter and the long length in the axial direction needs to be used (for example, see JP 2008-100272 A).
However, as shown in FIG. 7, in a roller hemming device 100 having a roller 101, which is the roller as mentioned above, with the small outside diameter and the long length in the axial direction, since flexure occurs at the time of the hemming because of the large interval between a part of the roller 101 coming in contact with the flange of the outer panel W11 to hem the work W, and an attachment member 102 to which the roller 101 is attached, it is difficult to hem the work W to a desired thickness. Moreover, since the big moment acts on the attachment member 102 at the time of the hemming, the problem occurs that the attachment member 102 is deformed for example. As a result, the time and cost required for the maintenance of the roller hemming device 100 increase.
On the other hand, because of the small outside diameter of the roller 101, when the roller 101 sequentially bends the flange of the outer panel W11, the elongation amount of the flange partly increases. As a result, the problem occurs that the flange is formed in waves for example.